This invention relates to certain novel Group 4 metal amidinate catalyst compositions and addition polymerization processes using the same. In particular the present invention relates to such polymerization processes that prepare polymers of vinylaromatic monomers having a syndiotactic stereostructure.
It is previously known in the art to prepare highly syndiotactic polymers of vinyl aromatic monomers by the use of Group 4 metal complexes containing a single cyclopentadienyl or substituted cyclopentadienyl group and an activating cocatalyst. Suitable, cocatalysts include alkylalumoxanes, inert, noncoordinating ion forming compounds, Lewis acids and mixtures thereof. Disclosures of such prior art processes are found in U.S. Pat. Nos. 5,045,517, 5,066,741, 5,206,197 and WO 92/05823 (equivalent to U.S. Ser. No. 07/740529, filed Aug. 5, 1991). The teachings of all of the foregoing patents and patent applications and publications is hereby incorporated by reference.
Recently (.eta..sup.5 -cyclopentadienyl)titanium benzamidinate dichloride and (.eta..sup.5 -cyclopentadienyl)titanium benzamidinate dialkyl complexes were shown to be useful in the polymerization of ethylene and propylene. A. N. Chernega, et al., J. Chem. Soc., Chem. Commun., 1993, 1415. Other researchers have prepared a variety of N,N'-bis substituted benzamidinato metal complexes. D. Fenske, et al., Z. Naturforsch, 1988, 43b, 1611, H. W. Roesky, et al., Chem. Ber., 1988, 121, 1403. The use of metal complexes containing only one amidinate moiety in the formation of addition polymerization catalysts, particularly catalysts for polymerization of monovinyl aromatic monomers to form syndiotactic polymers, has been previously unknown.